dsDNA

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Antigens

Deoxyribonucleic acid (DNA) as antigen may be either double-stranded (dsDNA) or single-stranded (ssDNA), but only dsDNA antibodies are specific markers. For use in anti-DNA assays, DNA from tissue, from eukaryotic cell, from bacteria or from bacteriophages is used. Circular plasmid DNA is a very suitable choice, because the risk to incorporate single strands is very low.

In the Varelisa and EliA assays the DNA is coated as recombinant plasmid double-stranded DNA.

Disease association, antibody prevalence and specificity

Systemic lupus erythematosus (SLE), dependent on method used and on the activity status of patients the antibody prevalence varies betwenn less than 30 to more than 90%. Anti-dsDNA antibodies belong to the ARA diagnostic criteria for SLE.

The disease specificity varies highly, dependent on the method used. With highly sensitive methods, anti-dsDNA can be found in uveitis, discoid lupus erythematosus, rheumatoid arthritis, juvenile rheumatoid arthritis and further in a wide variety of patients. In these cases, we are mostly dealing with antibodies of the IgM isotype of IgG with low avidity.

Disease activity

Good correlation of anti-dsDNA titer and disease activity, thus important for monitoring, especially high aviditiy IgG antibodies. A rise of the antibody titer can predict an exacerbation of the disease. Quantitative anti-dsDNA IgG should be measured regularly in SLE patients.

When is the measurement recommended?

Suspicion of SLE, monitoring of SLE.

Antibody isotypes

IgG. IgM is often determined, but the clinical significance in diagnosis and monitoring is reduced.

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Antigens

In their natural state, the small nuclear RNAs, also called U-RNAs (for "uracil rich RNAs"), exist as ribonucleoprotein particles (snRNP). The U1 snRNA is present as complex with the Sm proteins, which are found also in the U2, U4 and U5 snRNPs, and the U1-specific proteins 70 kDa, A (34 kDa) and C (22 kDa).

U1 snRNP complexes are primarily localized in the nucleoplasm and are involved in the splicing process.

Disease association, antibody prevalence and specificity

Anti-RNP may occur in 30-40% of patients with systemic lupus erythematosus (SLE). The SLE sera may be monospecific for anti-RNP but usually this antibody appears in conjunction with other antibodies specificities. Anti-Sm positive sera are almost always positive for anti-RNP, too.

Mixed connective tissue disease (MCTD) is defined by the presence of high titer anti-RNP (especially anti-70 kDa antibodies, but also anti-A and -C).

Anti-U1 RNP antibodies may also occur in a small fraction of patients with Sjögren's syndrome, rheumatoid arthritis, scleroderma, and polymyositis.

Disease activity

Longitudinal studies have indicated that anti-U1 RNP antibody titers vary over time, but it is uncertain whether these levels reflect underlying disease activity.

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Antigens

In their natural state, the small nuclear RNAs, also called U-RNAs (for "uracil rich RNAs"), exist as ribonucleoprotein particles (snRNP). The U snRNP U1, U2, U4, U5 and U6 all contain a group of proteins, the so-called Sm peptides, with the major targets being the B and D polypeptides. Because of cross-reactivity between the A, the C and the B/B' proteins, up to 60% of anti-U1 RNP sera may react with B/B'. Thus, only the presence of anti-D and/or the absence of anti-A and anti-C can be regarded as characteristic for an anti-Sm sera. Until now, all trials to produce an antigenic recombinant SmD protein with a good reactivity failed because of its very special structure. In 2004, an ELISA using a dimethylated SmD peptide was developed which showed to have a significantly higher specificity than traditional assays with purified SmD.

The EliA SmDP assay as well as the Varelisa Sm Antibodies assay are coated with a synthetic SmD3 peptide. The EliA Sm Well is coated with a purified Sm antigen.

Disease association, antibody prevalence and specificity

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by chronic inflammation of the connective tissue, affecting about 0.5% of the population worldwide. Sm antibodies are found in 5-30% of patients with SLE, depending on the ethnicity of the SLE population. Because of their high disease specificity Sm antibodies have been included in the American College of Rheumatology (ACR) criteria for classification of SLE.

Disease activity

When is the measurement recommended?

Suspicion of SLE.

Antibody isotype

IgG

Other detection methods

IIF on HEp-2 (punctate staining pattern throughout the nucleus; only the nucleolar regions are generally unstained). The immunofluorescence technique cannot distinguish between anti-U1 snRNP and anti-Sm antibodies. Other methods (e.g. counterimmunoelectrophoresis, immunoprecipitation; immunoblotting) can be used but are not necessarily useful for routine.

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Antigens

The SS-A/Ro particle contains a hY RNA (human cytoplasmic RNA) and associated proteins: a 60 kDa and a 52 kDa protein. The 52 kDa protein is not directly bound to the hY RNA but to the 60 kDa protein. It seems that 52 kDA protein is sometimes associated to the SS-A/Ro particle and sometimes not. The Ro antigen is found in the cytoplasm but also in the nucleus. The role of the SS-A/Ro particle in the cell is not known yet.

Our assays use human recombinant Ro 60 and Ro 52.

Disease association, antibody prevalence and specificity

Primary Sjögren's syndrome (60-75%), part of the diagnostic criteria

Secondary Sjögren's syndrome (about 80%)

Systemic lupus erythematosus, SLE (40-50%)

Mothers of children with neonatal lupus syndrome (100%), but only one in 50 children born to mothers with anti-Ro develop heart block.

Rheumatoid arthritis (2-10%)

Other autoimmune diseases (rarely, with sensitive methods)

Normal controls (0.5%)

Anti-Ro 52 kDa are frequently found in Sjögren's syndrome, whereas anti-Ro 60 kDa are observed more often in SLE.

Disease activity

Anti-Ro are reflecting the extension of the disease in Sjögren's syndrome and are associated in particular with the extraglandular manifestations and serologic findings of the syndrome. On the other hand, anti-Ro levels do not noticeably fluctuate with disease activity or with steroids and/or immunotherapy.

In SLE patients Ro60, Ro52 and La antibody profile is fixed at an early stage of disease and in most patients hardly changes.

SS-B/La

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Antigens

The La/SS-B is a ubiquitously expressed phosphoprotein with 47 kDa, that associates with a variety of small RNAs including the hY RNA of the SS-A/Ro particle. La probably is a transcription termination factor for RNA polymerase III and is found in the cytoplasm as well as in the nucleus.

Anti-La are almost always associated with anti-Ro and particularly the 52 kDa component.

Disease activity

Whether the titer of anti-La correlates with disease activity in Sjögren's syndrome or SLE is unknown. Detection per se of anti-La precipitins is a stable serological finding, which does not fluctuate during the course of disease.

Antibody isotypes

References

Ribosomal P

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EliA Rib-P -not for sale in the U.S.

14-5521-01

2 x 12 tests

Antigen

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized with multiple organ involvement resulting in disability and increased mortality. Antibodies against ribsosomal-P (anti Rib-P) react against acidic phosphorylated ribosomal proteins P0, P1, and P2 (with molecular mass of 38, 19, and 17 kDa, respectively) and are located on the S60 subunit of ribosomes. Anti Rib-P can be detected in approx. 15 to 20 % of patients with SLE. They appear highly specific for SLE; therefore, they can be used as diagnostic marker for the disease. Furthermore, association has been described with particular manifestations of lupus, especially with neuropsychiatric, renal, and hepatic involvements. However, results are conflicting regarding the existence of such associations, depending on different study set-up, different study population or different sensitivity of tests used for the detection of anti Rib-P.

Mi-2

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Antigen

There are two forms of Mi-2 proteins which show a high similarity (almost 70%): Mi-2α (208 kDa) and Mi-2β (218 kDa). Only Mi-2β seems to be the specific target for autoantibodies. Mi-2 seems to play a role in regulation of transcription. Mi-2β is a part of a nuclear complex named “nucleosome remodelling deacetylase (NuRD)”.

EliA Mi-2 Wells are coated with human recombinant Mi-2b protein produced in the baculovirus/insect cell system.

Disease association, antibody prevalence and specificity

15-31 % of adult dermatomyositis patients

Rare (<1 %) in polymyositis patients

More than 90 % of anti-Mi-2 positive patients have dermatomyositis.

The specificity of anti-Mi-2 is very high. In our validation study none of the 180 disease controls was positive.

Fibrillarin

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Antigen

Synonyms for Fibrillarin:

Scl-34

U3-RNP

rRNA 2'-O-methyltransferase

Fibrillarin, a 34 kDa protein, is the main component of the nucleolar U3-RNP complex, which is involved in pre-rRNA processing. Fibrillarin is also a component of other small nucleolar ribonucleoprotein complexes (snoRNP) and is also found in coiled or Cajal bodies.

EliA Fibrillarin wells are coated with human recombinant fibrillarin produced in the baculovirus/insect cell system.

Disease association, antibody prevalence and specificity

7-14 % of patients with scleroderma

Up to 64 % of patients with diffuse cutaneous SSc

Occur more frequently in a subset of SSc patients who are often of African descent (>50%), male, and with serious cutaneous and visceral disease. It is the second most ANA antibody in African American with SSc (after Scl-70).

Prognostic Marker

Markers for diffuse cutaneous SSc are anti-fibrillarin (up to 64 %), anti-RNA-Pol III (up to 85 %), and anti-Scl70 (up to 71 %), while patients with anti-fibrillarin have the worst prognosis, as they typically are associated with multiorgan involvement including small intestinal involvement, renal crisis, pulmonary fibrosis/pulmonary hypertension or muscle inflammation. Anti-fibrillarin positive patients are likely to develop alveolitis, pulmonary fibrosis and later on severe vascular pulmonary hypertension and need to be monitored.

Specificity

High specificity for scleroderma

Rare occurrence in SLE or Raynaud‘s phenomenon

Disease activity

There are no hints that the antibodies correlate with disease activity and could predict any relapse. Therefore, a regular follow-up testing after diagnosis is not recommended.